Surface discharge spark plug and method for making such a spark plug



April 23, 1957 w. B. SMITS 2,790,104

SURFACE DISCHARGE SPARK PLUG AND METHOD FOR MAKING SUCH A SPARK PLUG v Filed Jan. 18, 1952 INVENIOR {4 7725 55y: 5/?175,

QMRQM ATTORNEY United States Patent Surface discharge sparkplugs consist of two or more electrodes, between which there is an intermediate mass, on'thesurface of which the ignition spark slides.

This intermediate mass naturally has othermate'ria'l properties than the electrodes, and'in particular itsco efficient of expansion is usually smaller' than that ofthe" electrodes. This may result in an air gap being formed"- during operation between the electrodes and the intermediate mass, whichis highly undesirable-tonthe proper functioning-of the spark plug. The Netherlands p'atent specification No. 62,643 describes how this drawbaek z can be obviated: according to this patent specification an organic'substance is introduced separately into the sea'ms between the-electrodes and the intermediate-mass,:which:-. substance absorbs the above -rnenti0nedexpansion dif.- ferences, thus preventing the formationof an---air-gap For the generation of a surface discharge spark .it. is necessary thatthe intermediate mass should-have a-given surface conductivity and shouldalso preserve'thisazafter continued burning ofi. The Netherlands patent-specificae" tion No. 54,723 describes a number of measures to achieve this.

It is thus an object of the present application to dis- 1 close a surface discharge spark plug -utilizing-an-inter--- mediate'mass which both avoids the neediof-aneorganie" fillterfor resulting air gaps and achieves cont-inued.con--- ductivity for thedischarge spark. "It is further a put-*- pose of the present application to disclose various-materials and their characteristics a to accomplish the abovementioned objects.

According to the present invention ones'proceeds: asv follows. As basic material-for the intermediate mass use is made of asbestos, glassfibresor a similaramateriahw This forms-a continuous mass, whichis sufficiently elastic to prevent the formation of air'gaps asdescribedi abovea This-mass, which is preferably fibrous -is then impregnated with a substance or SllbSiflIlCCStWhiC'h oniithe onei hand fill up the-pores'or causethe formation-in -situ of such a fillingysubstance; and on the other hand: subsequentlyproduce the desiredsurface conductivitm Through the impregnation, the basic materialma-y alsow be chemicallymodifieduntil it. hasobtained more favourable properties.

Theaimpregnating agents be gaseous-or liquid? In the latter case they maybe either molten substances or col.- loidal or true solutions.

These and other features of the invention will become apparent from the-follc'awin'g 'sygiecification, taken-in conjunction with'the'r accompanying drawings, in which:

Fig. 1 is .a side elevational view, partly in section,.,o a plug manufactured in accordance with the invention};

Fig. 2Lis abottomplan'view-of theplugjshowniifiF-i 1;.1

In'ithe drawings, the "numeral 1 indicates the'lr'netalli body of the "spark'plu'g which acts as an outer electrode. Numeral '2" indicates the central electrode. A porcelain insulation 3"-separat'es' the inner and outer electrodes. T-he insulation 3 counects'the'"two"electrodes mechanically and "nointerveningair 'spa'c'esare left between the parts; The ins'ulator hason its end surface between "the "else-1 trodes, a special layerr4 of lthentypei referred to above, and which will be discussed in: greater detail belowtv-AS D I phsphate also have a similar effect.

Patented Apr. 23, 1957 All shdwnfthe' layer 4 does not extend beyondlthe frontsurfaces of "theelectrodes. v i 7 As indicated above, a fibrous mass 'suflici'ently' elastic to prevent the formationoffiair gaps is pressed into the area 4.- This mass then is impregnated with. substances to fi ll"iip"the pores and to. givejthe s'ur-fa'ce the desired conductivity. f I

One may, for example, press in 'a solution of concentrated chromic acid. Aninterme'diate mass impregnated inwthis :manner always has. suff cient surface .conductivity at. the. working temperature; The. same holds good for solutions of boric acid; an additional advantage is that through an appropriate temperature treatment boron silicates are formed with the asbestos, if the latter has been used a's-"basic material: Solutionso di'um' ammonium nfact', the chemi- I also comes within cal modifieatioifof 'the basic material" the 'sco'p'eof the invention;

However, one may also operate in stage's and cause a suitable substance to betformedin the pores. The basic material is, for example, fir st impregnated with a silver nitrate soliition and then with hydrochlo'ric' acid. The silver ehloride formed enters the pores,- and fa' 'surface con-i ductivity which is permanent, eve'n'rafter"continuedburning, is thus ensured.

It wasfound to b e.a very good method first to impregmate with a liquid low molecul'ar "'o rganici silicon! com-l pound. Treatment of theimass in the heatgives rise to polymerization and to the formation .of siliconfcom- T pounds: In the"ther'm"al decomposition during f o era: 5

:tiofig surface conductivity is produced. lnsteg of .using, j

low-molecular organic silicon compounds ready for use, one may also impregnateawithra number of basic substances in succession, from which the compounds mentioned areproduced in the. mass itselfi,

Onemay: first impregnate the 'bas'ictmaterialflinthe. mannerdescribed above, and. then insert it between-"the electrodes: It is, however, advisable first to construct the spark plug, at least in part, with the basic material between the electrodes, and'subsequently to press in the impregnating iagent(s) 1 under: pressure There is "naturally-no sense in pressing in for a longer-time or=apply inga higher pressure than is required to impregnate the pores-ofthatsectioh of the basicmaterial' and lor to effect chemical modification of more than the section lying between the active partsof the: electrodes. It is obvious that the. last-mentioned methodi. e. .impregnat ion 'inr the sparktplug' ,when already (partially) assembled-,-- is: pessible" in particular -when .the intermediate mass per -se r already possessed. sufficient elasticity" and plasticity .--to be applied properly. The impregnation then merely serves to produce the surface conductivity.. Finallyg-it .-isalso obvious that the basic materialwhich--is.; preferablwv fibr0us-can first be partially impregnated, outside the spark plug, to ensure good elasticit y and plasticity, and can then, afterbeing fittedin the .spark; plug, 1be impregnatedjfurther "to produce good 'surface-conductivity:F A number of examples will--begiven to explain the" invention more in detail, without, however, its being restricted thereto. To this end a spark plug element was :filled with fibrous materials, such asasbestos, glass-wool or heat-resistant. fibrous materials which had .alreadybeenpartially prepared, and the impregnating agent was-subsequent1'y"pressed'in or inserted by the applicationaof 'a vacuum.

chr m'ieacid isremoved;.andvthomass is dried *for. about 1 Example II A saturated solution 'of 'chromic acid is pressed in for about 5 minutes under a pressure of 4 at., and imme diately afterwards a solution of lead nitrate is pressed in for about 15 minutes under a pressure of 6 at.; the mass isdried for about two hours at about 90 Example 111 L A saturated solution of boric acid is pressed in for 1-30 minutes under a pressure of 0-20 at.; the mass is dried for one hour at 140 C.

-Example- IV A solution of sodium acetate ispressed in for Sminutes under a pressure of 4 at., and the mass is dried for'one hour at 140 C.

Example V i .A solution of sodium acetate is pressed in for 5 minutes under a pressure of 4 at. When the mass has been dried for one hour at 140 C., it is burned oil with a hydrogen An alkylphenolformaldehyde condensate is pressed. in

. for minutes at 10 at., and the mass is then baked for one hour at 200 C.

Example XVI An alkylphenolformaldehyde condensate is introduced.

into the mass, first under vacuum and then by the application of pressure; this double treatment is repeated once flame in such a manner that the surface ofthe mass has a temperature of 300 C.

' Example VI An alkylphenolformaldehydecondensate is pressed in for 10 minutes at 10 at., and-themass is subsequently baked for one hour at 240 C. I j

Example VII A mixture of 50% of dimethyl silicon trichloride and 50% of methyl-silicon trichloride is pressed in for 10 minutes at 6 at. After this the element is suspended in steam for 15-60-minutes, upon which it is dried for 1-10 hours at 240 C. If desired, steam under a pressure'of 4 at. can be used for this. V

Example VIII A heat-resistant varnish on a basis of silicon compounds is introduced into the element by the application of a vacuum for minutes and subsequently by pressure -A lead nitrate solution is introduced into the element for 5 minutes under a pressure of 4 at., and subsequently a solution of 10-20% hydrochloric acid for 15 minutes under a pressure of 10 at., upon which the mass is dried for one hour at 140 C.

more, and the mass is then baked for one hour at 240 C.

Example XVII The treatment was the same as in Example VII, but in this case, as has been stated, the mass consisted of mica.

. Example XVIII The element is introduced for 45 minutes into a separate space under a vacuum of about 0.1 mm. mercury, and subsequently a heat-resistant varnish on a basis of silicon compounds is admitted into the space, pumping is continued for another 5 minutes, the mass is then brought under a pressure of 2-4 at., which is maintained forone hour, it is dried for one hour at 120 C., and then baked for 10 hours at 250 C.

I claim:

1. A spark plug of the surface discharge type comprising a pair of spaced electrodes, semi-conductive means disposed between said spaced electrodes, said semi-conductive means forming a discharge surface for the passage of a spark between the electrodes, said semi-condu'ctive means comprising an elastic fibrous material, the pores of the fibrous material being filled with a substance which has no detrimental effect on the elasticity and plasticity of the intermediate mass and which maintains the conductivity of the mass.

2. A spark plug according to claim 1 wherein the substance filling the pores is chromic acid.

3. A spark plug according to claim 1 wherein the substance filling the pores is boric acid.

4. A spark plug according to claim 1 wherein the substance filling the pores is sodium acetate.

5. A spark plug according to claim 1 wherein the substances filling the pores are lead nitrate followed by a.

The hydrochloric acid may also be introduced into the mass under a pressure of 6 at.

' Example XI A solution of fairly concentrated silver nitrate is introduced for 5 minutes at '4 at., and the mass is subsequently dried for one hour at 140 C. i

Example XII Example XIII A solution of silver nitrate is pressed in for 5 minutes at 4 at. and subsequently a solution of 10-20% hydrochloric acidfor- 15 minutes at 6 at., upon which-the is'dried .for one hour at 140' C.

strong acid of the class comprising sulfuric acid and hydrochloric acid.

6. A spark plug according to claim 1 wherein the substance filling the pores is silver nitrate.

7. A spark plug according to claim 1 wherein the substance filling the pores is an alkyl phenol formaldehyde condensate.

References Cited in the file of this patent UNITED STATES PATENTS 

